1. Field of the Invention
The present invention is concerned with an improved harmonic phasing device adapted for installation on a variety of web-handling stations such as printing presses or similar equipment, in order to permit selective adjustment of the angular or circumferential disposition of one or more of the web-engaging rollers associated with such equipment. More particularly, it is concerned with a phasing unit preferably in the form of a compact, self-contained, dual harmonic gear unit which serves as a drive transmission during normal operating conditions, and includes a selectively operable stepper motor which can be actuated for circumferentially shifting a roller to achieve proper registration with other in-line web-contacting rollers in the press.
2. Description of the Prior Art
Traditionally, complete web-fed offset lithographic printing presses are composed of a series of aligned stations or towers through which a continuous web of paper is fed for printing and handling purposes. In the case of color printing for example, a separate printing tower is used for each color so as to give the final printed material a multi-color effect. In addition, a complete press may include numbering and/or punching units, as well as slitting and folding devices.
Printing presses are generally either of the hard impression cylinder or perfecting variety. A hard impression press includes one or more printing towers each including a pair of web-receiving rollers, i.e., a printing roller and hard impression roller arranged to present a web-receiving nip therebetween. Printing with this type of apparatus is on one side of the web only. Perfecting presses on the other hand are designed for simultaneously printing on both faces of a moving web. To this end, the towers of a perfecting press include a pair of adjacent blanket rollers designed to receive the web therebetween and to print on both faces thereof. Each web has an associated plate cylinder for transferring the image to be printed onto the associated blanket roller.
As those skilled in the art will readily appreciate, an extremely important feature in connection with multiple-station web printing and handling equipment is that proper registration be maintained between respective stations. For example, in the case of multi-color printing wherein each successive printing tower prints a separate color, it is all important that precise registration be maintained so that blurring and overlapping of the successively printed images be avoided. Accordingly, a number of proposals have been made in the past for circumferential adjustment of one or more rollers in a given press tower or station relative to the rollers in separate towers, and, in the case of a perfecter unit, relative to other rollers in the same unit. Generally speaking, prior mechanisms for such circumferential adjustment have been quite intricate, and moreover require a considerable degree of operator skill. Many such units demand manual operation, and are limited in their ability to circumferentially adjust a roller (often referred to in the art as phase adjustment or change) only through an arc of a few degrees. Accordingly, both the accuracy and range of utility of such prior devices are limited.
Prior printing presses have employed harmonic phasing devices without utilizing the advantages of the 1:1 harmonic drive differential. For example, in U.S. Pat. No. 3,724,368, the harmonic drive input member has a predetermined number of internal gear teeth and the output member has a number of external gear teeth less than the predetermined number of internal gear teeth on input member; compensation for the difference in number of gear teeth is needed outside of the harmonic drive unit, so that the plate cylinder is rotated at the surface speed of blanket cylinder.
It has heretofore been suggested that so-called harmonic or sine wave gears be adapted to the adjustment of phase relationships between printing rollers. Harmonic gearing is described in U.S. Pat. No. 2,906,143 to C. W. Musser, U.S. Pat. No. 3,565,006 to Stewart, and in an advertizing brochure distributed by the United Shoe Machinery Corporation entitled "Harmonic Drive Pancake Gearing", HDUF 13000-76. All of the aforementioned are incorporated by reference herein. Generally speaking however, a harmonic drive gear includes a rotatable, elliptical wave generator, along with a flexible, toothed, rotatable spline disposed about the wave generator, and first and second rigid, annular, internally toothed, rotatable splines about the flexible spline and located for engagement therewith. One of the rigid splines is generally referred to as a dynamic spline, and has the same number of teeth as the flexible spline. The other rigid spline is referred to as the circular spline, and has a greater number, e.g., two, of teeth than the flexible spline. In operation, rotation of the wave generator results in a continuously moving wave form transferred to the surrounding flexible spline, and thence to the outermost rigid splines.
It has also been suggested in the past to employ a pair of harmonic drive gears mounted in adjacent, intercoupled relationship as a 1:1 transmission and phase changing differential. In such propsals, the tandem harmonic drive gear components are of the same size and ratio. Moreover, one of the wave generators is held fixed, whereas the other wave generator is selectively rotatable for phase changing purposes.
Prior patents of background interest to the instant invention include, in addition to the foregoing referenced patents, U.S. Pat. Nos. 3,218,696, 1,590,742, 1,320,358, 2,248,926, 3,511,179, 2,949,851, 3,073,997, 2,301,379, and 3,525,305.